Machines that continuously and automatically produce large quantities of flake ice are well known for use by the food processing industry, fishing industry, within grocery food stores, and for cooling concrete in construction to name a few. Flake ice machines have been developed that utilize a rotating cooling disk that is cooled by flow of a refrigerant through internal passages formed in the disk. Water or other liquid to be frozen is introduced to a portion of the side surfaces of the rotating disk, is sub-cooled, and is then removed as the disk rotates between a pair of ice removal blades positioned adjacent the side surfaces of the disk. An example of such a conventional flake ice machine is disclosed in U.S. Pat. Nos. 5,307,646 and 5,448,894 to Niblock, the disclosures of which are hereby expressly incorporated by reference.
In such conventional flake ice machines, the ice removal blades must not contact the side surfaces of the disk. Such contact results in rapid wear of the removal blades and/or disk which is unacceptable from both a maintenance and sanitary point of view. Simultaneously, the ice removal blades should be positioned as close to the disk side surfaces as possible to facilitate complete removal of ice from the disk surface each revolution. Any increase in blade spacing from the disk increases the likelihood of incomplete ice removal. If the blade/disk spacing is too great the blades will shear through the ice leaving a hardened layer or bumps of ice on the disk. The buildup of ice under the ice removal blades causes extra pressure, pushing the disk against the blades. Thereafter, the blades tend to push against this strongly adhered ice and cause deflections in the disk and resultant tool wear which compounds the problem. These type of stresses, as well as repeated thermal expansion and contraction stresses, can lead to permanent warpage of a disk, in the radial direction, out of the nominal plane of either disk cooling surface and render the machine nonfunctional.
Many conventional flake ice machines can only feasibly produce ice from soft water when a small quantity of salt has been added. The salt facilitates complete removal of ice from the disk side surfaces in large flakes. A salinity of 150-1,000 ppms, and most typically 250-500 ppms, is conventionally utilized to facilitate ice removal. Conventional flake ice machine may be outfitted with resiliently mounted blades or flexible blades for use in making salt-containing ice. The use of flexible or resiliently mounted blades is intended to eliminate or to permit reduction in the clearance between the blades and the disk. However, the use of salt is often undesirable for ice used for some purposes. Because fresh water ice is more difficult to remove, and particularly to remove in desirably large flakes rather than smaller pieces and fines, a rigidly mounted blade must be utilized to withstand the required shear force without yielding. Consequently, many conventional flake ice machines are not suitable for producing pure fresh water ice.
Previous flake ice machines that are suitable for producing fresh water ice maintain a clearance of approximately 0.010 to 0.012 inches between each rigidly mounted blade and the corresponding disk surface. Two factors have prevented smaller clearances. First, the disk is welded to the hub of a shaft for rotation about the central axis of the disk. As with all manufactured parts, disks tend to exhibit some axial runout, which causes the circumferential edge of the disk to wobble during rotation. Second, as noted above, the disks often flex during ice removal. The blade removal clearance must account for both of these factors to prevent blade/disk contact.
The refrigerant passages in conventional disk designs and manufacture used for both fresh and salt water ice manufacture exacerbate the problem of disk warpage. These disks include internal cooling passages that result in a relatively thin disk having low strength, particularly in the radial direction. Such conventional disks are manufactured using a chemical etching process to form the flow passages in the disk. The manufacture of conventional disks using a chemical etching process contributes to the disk's overall weakness by limiting its thickness. The chemical etching process removes material equally from both sides and the bottom of the passages. Therefore, the passage depth is limited to the design width. Otherwise, all the passages would run together. This fact limits the thickness of each disk half to the passage depth plus the thickness of the freezing surface after machining. For conventional disks, the total thickness of the assembly is typically less than 1/4".
Regarding radial weakness of the conventional disk designs, U.S. Pat. No. 5,157,939 to Lyon et al. discloses a flake ice machine having numerous internal refrigerant passages. The disk is formed from two mating disk halves, each of which includes a plurality of chemically etched grooves on its internal surface. The pattern of the grooves in the two halves are mirror images, so that when the halves are mated and brazed together, corresponding grooves mate to form passages. The individual grooves are separated by narrow walls. The grooves are of a depth such that only a thin layer of disk material remains between the bottom of the groove and the outer cooling surface of the disk, for efficient heat transfer from the coolant. The primary structural strength of the disk is thus provided by the walls between the grooves.
The passages of the Lyon disk are arranged so that all of the passages have substantially the same length for achieving a uniform pressure drop in each passage, and so that all points on the disk side surfaces are close to the refrigerant. This attempts to ensure uniform cooling along the disk side surfaces and to prevent "hot" spots. To achieve this result, all of the initial portion of the passages extend radially outward a predetermined distance and then turn to run circumferentially for a substantial portion of their length before turning back in towards the disk hub.
The net result is that there are large portions of the radial segments of the disk, particularly at 90.degree. to the inlet and outlet passages and extending towards the disks outer circumference, that include only circumferentially oriented passages, and not radially oriented passages. This arrangement results in the disk being significantly weakened in the radial direction, because the walls between the disks lend their rigidity and strength only in the circumferential direction in these disk segments. The ability of the disk to withstand temporary bending and permanent warpage, especially at the periphery of the disk, is substantially lessened by this passage arrangement. Moreover, dynamic forces that tend to cause warpage and bending, such as ice removal blade stresses due to disk wobble or incomplete ice removal, are greatest at the disk periphery.
Another drawback of conventional disk design is the possibility that one or more of the passages will become blocked with evaporated refrigerant, essentially becoming short circuited. Any blocked passages are thereafter not useful in disk cooling. Additionally, during manufacture of the disk, if the disk halves are not accurately matched during mating, cooling groove misalignment results and the disk is unusable.